The present invention relates to a centrifuge which is suitable for use in centrifugal separation, sedimentation or the like of small samples.
In the kind of centrifuges employed in the past for this purpose, as disclosed, for example, in Japanese Pat. No. 13839/62, the rotary shaft of a motor is inserted into an inner housing, a tube rack support or what is called a rotor is mounted on the rotary shaft in the inner housing, a plurality of test tubes are placed in the rotor radially of the rotary shaft. By driving the motor at high speed, the test tubes are rotated to apply centrifugal force to the samples in the test tubes for separation and sedimentation. In such a conventional centrifuge, since the test tubes are exposed in the inner housing during the high-speed rotation, the temperature of the test tubes is likely to rise due to air resistance to exert influence on the samples. Furthermore, since the test tubes are subjected to a large air resistance by such high-speed rotation, it is necessary to rotate the test tubes against the large air resistance; accordingly, a large drive power is required of the motor to compensate for what is called a windage loss and the power consumption of the motor naturally increases. In addition, there is a problem of noise which is generated by the test tubes while being rotated at high speed.
To avoid such defects, it has been proposed to dispose a container in the inner housing and place tube racks carrying test tubes in the container. In this case, however, a centrifugal force of the tube rack is applied directly to the container and the centrifugal force is very large, so that the container must be mechanically strong. Accordingly, the container is made of metal and thick and its moment of inertia is large. Also for driving such a container itself, a motor of large power is needed and it is difficult to rapidly accelerate and stop the container.
There has been proposed a centrifuge in which, when the rotor is driven at high speed, air is driven by the rotating rotor to decrease the air pressure in the vicinity of its center of rotation and air is drawn into the centrifuge from an air inlet port formed in its lid in opposing relation to the center of rotation of the rotor, the air drawn through the air inlet port being directed around the rotor to cool it. This arrangement permits easy cooling of the rotor but has the defect that noises are produced in the neighborhood of the air inlet port.
It is an object of the present invention to provide a centrifuge in which test tubes are not subjected to a large air resistance and hence do not greatly rise in temperature nor do they produce noises and which is small in windage loss and consequently permits the use of a motor of small drive power.
Another object of the present invention is to provide a centrifuge in which the rotor is relatively lightweight and hence can be driven by a motor of relatively small power to reduce the overall power consumption.
Still another object is to provide a centrifuge which is adapted to draw air therein to cool the rotor and test tubes, and which is less noisy.